InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Need & requirements for electrical grounding systems: this document discusses the details of why we need grounding, and definitions of electrical grounding and electrical bonding (what's the difference between these two terms.

“Grounding”, article 250 in the NEC, is probably one of the most difficult of the often used articles. In 2005 article 250 became “Grounding and bonding”.

In the 2008 NEC there has been a major revision in language, and phrases like “shall be grounded” have changed to “shall be connected to an equipment grounding conductor.” - Sketch courtesy of Carson Dunlop Associates.

Here we define electrical ground, grounding, bonding, and earthing terms and explain why there are important differences among these words.

Why we need electrical grounding

Speaking first a bit loosely (we'll get careful and detailed in a minute) the grounding system at a building provides an easy path for electricity to flow to earth should certain problems occur (a power surge, lightning strike).

Bonding or connection in the electrical panel between the neutral wires, ground wires, and the utility company's incoming neutral wire allowing current to flow to the utility company's wiring, assuring that a circuit breaker will trip or fuse will blow should a problem occur such as a short circuit or overloaded circuit.

Properly operating these overcurrent devices help prevent fire and shock.

Should an electrical fault occur where no neutral connection to the utility company or no local ground path is present, the electrical potential is just sitting there waiting for a person to come along, touch some component of the system, and by accidentally providing a path to earth through their body, receive a burn or potentially fatal shock.

Details of why we need grounding, and definitions of electrical grounding and electrical bonding (what's the difference between these two terms) can be read at Why Grounding is Needed.

Bud, a master electrician from Minnesota has offered these important clarifications:

"Grounding" has 2 main functions.

One is to provide a path to trip a breaker in the event of a 'short'
as in the text above. That function relies on a "ground"-to-neutral
connection required at services in the US (the "main bonding jumper").
The path is (branch circuit ground wire) to (N-G bond at the service)
to (service neutral) to (utility power transformer).

This path *must*
be metallic back to the power transformer to provide low resistance to
trip a circuit breaker. This function will work even if the service is
not connected to earth. And the NEC *does not allow* earth to be used
as part of this path.

One reason is the resistance of an earth path is too high. Assume the
earthing is only through a ground rod and the rod has a quite good 10
ohms resistance to earth. Further assume there is a 'short' connecting
hot to "ground". The current to earth will be 12A.

There is a good
chance this won't even trip a 15A circuit breaker. If the circuit is
loaded the breaker will trip, but after a significant time delay. In
the mean time, the "ground" potential with respect to the earth away
from the ground rod will be 120V.

Note that if you are using the earth as in the quote above, the path
is not just into the earth. It is back to the power source, and also
depends on the earth connection at the power transformer.

This would be better termed a *bonding* function.

Carson Dunlop's sketch shows how the electrical current in a building can find its way to earth by way of the electrical grounding system.

Why We Need Electrical Grounding in buildings

Electrical “Grounding” has two jobs in a building: an “earthing” and a “bonding” function.

What is Electrical Grounding? "Earthing"

A major purpose of “grounding” is to provide a path so a “short” will trip a breaker. That requires a low resistance path back to the power source, which is the utility transformer. The path relies on a neutral-ground connection required at all [not entirely true] services.

The second "grounding" function is actually a collection of three safety functions:

minimize the voltage between exposed metal and the earth

minimize the voltage between the power wires and the earth

provide a sink for lightning, power line crosses, and similar hazards

The 1st grounding function described above is accomplished by connecting the grounding conductors at the service to an earthing electrode.

The 2nd grounding function described above is accomplished by connecting the power neutral (the neutral wire entering from the utility company's service) at the service to an earthing electrode (ground rod). Provided it's a real earthing electrode not a fake one as we found in our photo (left).

The 3rd grounding function described above is accomplished by both of the above.

Practically, all three grounding functions are accomplished by a required neutral-ground connection at the power service, with the combined neutral-ground connected to an earthing electrode or electrodes.
This function might best be called “earthing”.

What is Electrical Bonding? Why is it Important?

The path is from a ground conductor [which is not necessarily a wire] to the service panel, through the neutral-ground connection, and back to the transformer via the service neutral. To provide high current to trip a breaker this must be a metal path.

The earth is far too high in electrical resistance and is not allowed to be the path. In fact this function will work if the service is not connected to earth.
This function might best be called “bonding”.

Connecting exposed metal together to minimize voltage between surfaces is also a “bonding” function.

There might be some virtues to showing the Neutral-to-Ground bond (called the main bonding jumper). As I wrote previously, it is barely visible in the Carson Dunlap diagram (above) with “Electrical path for ground and neutral wires”.

When a professional examines the interior of a main electrical panel, she looks to see if there has a strap for the bond between neutral and ground buses and to the grounding conductor leading to the earthing rod (ground rod). In some panels such as SquareD the bond is a screw (and very hard to identify if you don’t know what to look for - some home inspectors have trouble finding Neutral-Ground bonds.)

Reader Questions Requirement for Bonding the Electrical Ground System to the UFER or Re-Bar in a Foundation

4/26/2014
My electrician said he installed two grounding lines outside new house but inspector is making him connect 3rd rebar to basement electrical box. The problem is the rebar that was supposed to be installed with foundation wall is nowhere to be found.

Electrician says he never saw it and feels the outside is sufficient.

The [electrical] inspector assumes it was installed and must have gotten cut by framers. So he told electrician to hammer basement until he can find the rebar and connect pipe to it, then connect to electrical box. Wouldn't it be safer to drill a hole and insert new rebar rather than smash the entire basement?

Do you have any options for this disaster that is preventing passing electrical inspection that is needed ASAP. Who would be able to fix this, anyway and how? Do you know any workarounds?

Reply: approaches to finding re-bar in concrete footings or foundations

OPINION: A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone and such an inspection or a conversation with your electrical inspector may clarify why the demand you describe is being made - if it is being made really in the way stated.
That said I offer these comments:

This sounds as if the electrcial inspector has something in mind that we may be missing. The National Electical code provides several approaches to grounding, some are alternatives.
But the local code official is the final authority by law.

So if you must proceed to find the re-bar, instead of tearing up all of the concrete I can think of other approaches that may be much less disruptive:

1. Look at the building plans and specifications for the re-bar placement schedule. Making a test cut, possibly even from outside at the footings or inside at the footings or edge of slab one ought not have to go more than inches, certainly less than a foot in a direction that crosses the re-bar placement to find it by cutting an opening.

The idea that you'd have to tear up the whole structure sounds both exaggerated and unnecessary. If in fact you ended up tearing up more feet of concrete than the plans would suggest necessary, you've discovered that the builder omitted the steel reinforcement called for by plans - which itself would be a significant concern.

[Some non-structural slabs use fiber reinforced concrete and not re-bar, others use wire mesh, not re-bar, but re-bar would be expected to be in footings and piers regardless]

2. Hire an expert who has or rent a metal detecting machine that an locate steel in concrete to find the re-bar location closest to the required connection.

By "Ufer" we refer to the UFER ground (concrete encased grounding electrode) cited at DEFECTS LIST - ELECTRICAL SYSTEM and explained at ELECTRICAL DEFINITIONS. "Ufer" in my book refers to underground ferrous rod. This approach to electrical grounding improves the ground connection to earth in areas where soils are so dry that otherwise grounding may be ineffective.

You didin't indicate your location, but perhaps the electrical inspector knows that in your area it may be particularly important that the UFER grounding approach is used.

While we have frequently updated and added to the material, in its original form this information was presented by
Daniel Friedman - InspectAPedia.com, at the Hudson Valley chapter of the American Society of Home Inspectors -
HVASHI Seminar 12 Sept 2002, Updated April 2006. Sketch at page top courtesy of Carson Dunlop Associates.

Frequently Asked Questions (FAQs)

Question:

(Jan 28, 2013) eleCtriCian123 said:

I have one leg of my a feeder that reads 120 and the other is reading 50v....I have a grounding or a neutral issue CorreCt?

Reply:

I don't assume that Ele. A bad connection, a transformer problem or other snafus could also explain your voltage reading. But I'd certainly start at the local wiring at and in the building, at the SEC and at the meter.

Question:

(Feb 15, 2013) Anonymous said:

hi have overhead supply so no ground cable assuming i can get a good earth (on bed rock )is that all i need to pull down the house earth which is at moment unconnected at fuse board and floating at live(hot) voltage but hopefully with very little current available

i'm at the moment residing in Portugal but assuming that all country have same common system

Reply:

An overhead supply normally incldes a neutral wire that also is ultimately grounded by the electrical supplier.

I'm not sure it's correct to assume that all "bedrock" gives a good electrical ground. On the contrary it may be necessary to find enough soil at a high enough moisture level to give good electrical grounding, or it may be necessary to use multiple grounding electrodes or ground points.

We agree that leaving the home with no ground is extremely dangerous.

...

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com

John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net

The Home Reference Book, a reference & inspection report product for building owners & inspectors.Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.

The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.

Special thanks to Bud - a master electrician in Minnesota who contributed text and suggestions for explaining why we need electrical grounding, and for discussing the shortcomings of neon testers and plug-in receptacle testers - 1/22/2009

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. (courtesy of Amazon.com)

"Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]

"Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.